Candy’s Dandy, but Pot’s Scary

WE know that occasionally people react badly to marijuana. Some withdraw into anxious, glassy silence. Some responses are more horrifying. In a recent, much discussed case, a Denver man bought cannabis-infused Karma Kandy and hours later — perhaps after also taking prescription pain medication — began raving about the end of the world and killed his wife.

Marijuana is more dangerous than many of us once thought. For one thing, cannabis use is associated with schizophrenia, an often devastating disorder in which people can hear disembodied voices that sneer, hiss and command. A 1987 study published in The Lancet, the London-based medical journal, followed more than 45,000 Swedish military conscripts. Those who said on a conscription questionnaire that they had used cannabis more than 50 times were six times as likely, 15 years later, to have been diagnosed with schizophrenia than those who said they had not used it. There have been many more research papers since. A 2007 meta-study, also published in The Lancet, examined a series of them and concluded that there was a consistent increase in the incidence of psychosis — the radical disconnect from reality characteristic of schizophrenia — among people who smoked marijuana, with most studies showing a 50 to 200 percent increased risk among the heaviest users.

The causal arrow is complicated here. This does not prove that marijuana brings on schizophrenia. It could be that people with incipient schizophrenia are drawn to cannabis. But it is clear that cannabis can lead to passing paranoid and hallucinatory experiences, and a 2014 psychiatric overview argued that cannabis could not only cause those symptoms to persist, but to develop into a condition that looks like schizophrenia. Jim van Os, a leading European schizophrenia researcher, suggested that marijuana might be responsible for as many as one in seven or eight cases of schizophrenia in the Netherlands.

To be sure, that increased risk is pretty low: About one in 100 people will develop schizophrenia. The unnerving question is whether in this country, with its history of gun violence and its easy access to guns, a person with a paranoid reaction is more likely to act violently.

A basic anthropological insight about drugs and alcohol is that the effect of a drug is a result not just of biology, but also of culture. The classic argument on this is “Drunken Comportment,” a 1969 book in which Craig MacAndrew and Robert B. Edgerton said that the effects of alcohol depended on local expectations. They wrote that when Americans drank, they fought, argued and were much more relaxed about sex.

When American undergraduates get drunk, they throw sofas out of the frat house and wake up next to people they didn’t think they knew. That’s because we Americans think that alcohol is disinhibiting and that we can’t really control what we do.

That’s not necessarily the case in other cultures. Mr. MacAndrew and Mr. Edgerton gave example after example of people in other cultures who drank plenty of strong alcohol but didn’t behave as Americans did when drunk. In these societies drunks became silent, “thick-lipped,” or they grew talkative, but not violent. In some settings, the anthropologists were able to demonstrate that when drunk, people became violent in culturally rulebound ways.

When Mr. Edgerton was doing fieldwork in Kenya in 1962, for example, he was warned about a man who became dangerous when drunk. But when he encountered that man during a drunken episode, “the man calmed down, and as he walked slowly past me, he greeted me in polite, even deferential terms, before he turned and dashed away.” The drunk role did not include being violent to visiting anthropologists.

How people act when drunk, these anthropologists argue, is a learned behavior. People learn what it is to be drunk and what drunkenness permits.

Since then, anthropologists have demonstrated that this principle applies — to some degree — to the experience of many different drugs. As Eugene Raikhel of the University of Chicago summarizes the literature, drug experience is determined not only by the body’s chemistry but also by local ideas about what those drugs should do.

Right now, for many people, marijuana conjures up the mellow calm of the Rocky Mountain high. But that mellowness is associated with a set of cultural cues that may not be shared by all who buy legal cannabis. Alcohol is a factor in about 40 percent of violent crimes, according to surveys of perpetrators. Let’s hope that the meaning of being high doesn’t migrate.

T. M. Luhrmann, a contributing opinion writer, is a professor of anthropology at Stanford.